U.S. patent number 6,693,306 [Application Number 10/200,695] was granted by the patent office on 2004-02-17 for structure of a light emitting diode and method of making the same.
This patent grant is currently assigned to United Epitaxy Company, Ltd.. Invention is credited to Tzer-Perng Chen, Rong-Yih Hwang, Charng-Shyang Jong, Cheng-Chung Young.
United States Patent |
6,693,306 |
Chen , et al. |
February 17, 2004 |
Structure of a light emitting diode and method of making the
same
Abstract
A structure of a light emitting diode (LED) and a method of
making the same are disclosed. The present invention is suitable
for the light emitting diode having the area that is larger than
100 mil.sup.2 and having the insulating substrate, and is featured
in that the P electrode and the N electrode are mutually
intercrossed. With the use of the present invention, the light
emitted by each individual unit chip is more even; the operating
voltage of the device is reduced; the cut size of the device can be
enlarged arbitrarily according to the size of the unit chip; and
the light emitting efficiency is increased.
Inventors: |
Chen; Tzer-Perng (Hsinchu,
TW), Hwang; Rong-Yih (Hsinchu, TW), Jong;
Charng-Shyang (Hsinchu, TW), Young; Cheng-Chung
(Changhua, TW) |
Assignee: |
United Epitaxy Company, Ltd.
(TW)
|
Family
ID: |
30443557 |
Appl.
No.: |
10/200,695 |
Filed: |
July 22, 2002 |
Current U.S.
Class: |
257/99; 257/88;
257/91; 257/96; 438/28; 438/29; 438/34 |
Current CPC
Class: |
H01L
33/38 (20130101); H01L 33/08 (20130101); H01L
33/20 (20130101); H01L 2933/0016 (20130101) |
Current International
Class: |
H01L
33/00 (20060101); H01L 029/22 () |
Field of
Search: |
;257/99,88,91,95,96,97,98 ;438/28,29,34,38,39,42,43 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Crane; Sara
Attorney, Agent or Firm: Webb Ziesenheim Logsdon Orkin &
Hanson, P.C.
Claims
What is claimed is:
1. A structure of a light emitting diode (LED), comprising: a
substrate; a semiconductor epitaxial structure, comprising an
N-type semiconductor layer, an active layer, P-type semiconductor
layer and a transparent contact layer, wherein the N-type
semiconductor layer covers the substrate, and a plurality of
extrusions are formed on a portion of a surface of the N-type
semiconductor layer, and a channel is formed between the every two
adjacent extrusions of the plurality of extrusions, and the active
layer, the P-type semiconductor layer and the transparent contact
layer are sequentially stacked on the plurality of extrusions; an
N-type electrode layer which adheres to the N-type semiconductor
layer and is located in the channel; a plurality of P-type
electrodes located above the transparent contact layer; an
insulating layer covering the transparent contact layer and the
N-type electrode layer, wherein a portion of the N-type electrode
layer is exposed to be an N-type pad; and a conductive layer which
covers the insulating layer and is connected to the plurality of
P-type electrodes, wherein at least one P-type electrode of the
plurality of P-type electrodes is a P-type pad.
2. The structure of the light emitting diode according to claim 1,
wherein the material of the substrate is selected from a group
consisting of sapphire and glass.
3. The structure of the light emitting diode according to claim 1,
wherein the shape of the extrusions is rectangular prism.
4. The structure of the light emitting diode according to claim 1,
wherein the material of the N-type semiconductor layer, that of the
P-type semiconductor layer, and that of the active layer are
selected from a group consisting of GaN, AlGaN, InGaN, and
AlInGaN.
5. The structure of the light emitting diode according to claim 4,
wherein. the active layer has a double hetero-junction
structure.
6. The structure of the light emitting diode according to claim 4,
wherein the active layer has a quantum well structure.
7. A structure of a light emitting diode, comprising: a substrate;
an N-type semiconductor layer covering the substrate, wherein a
plurality of extrusions are formed on a portion of a surface of the
N-type semiconductor layer, and a channel is formed between every
two adjacent extrusions of the plurality of extrusions; an active
layer covering the extrusions; a P-type semiconductor layer
covering the active layer; a transparent contact layer covering the
P-type semiconductor layer; an N-type electrode layer which adheres
to the N-type semiconductor layer and is located in the channel; a
plurality of P-type electrodes which adheres to a portion of a
surface of the transparent contact layer; an insulating layer
covering the transparent contact layer and the N-type electrode
layer, wherein a portion of the N-type electrode layer is exposed
to be an N-type pad; and a conductive layer which covers the
insulating layer and is connected to the plurality of P-type
electrodes, wherein at least one P-type electrode of the P-type
electrodes is a P-type pad.
8. The structure of the light emitting diode according to claim 7,
wherein the material of the substrate is sapphire.
9. The structure of the light emitting diode according to claim 7,
wherein the material of the substrate is glass.
10. The structure of the light emitting diode according to claim 7,
wherein the shape of the extrusions is rectangular prism.
11. The structure of the light emitting diode according to claim 7,
wherein the material of the N-type semiconductor layer, that of the
P-type semiconductor layer, and that of the active layer are
selected from a group consisting of GaN, AlGaN, InGaN, and
AlInGaN.
12. The structure of the light emitting diode according to claim
11, wherein the active layer has a double hetero-junction
structure.
13. The structure of the light emitting diode according to claim
11, wherein the active layer has a quantum well structure.
14. A method of making a light emitting diode, comprising:
providing a substrate; forming an N-type semiconductor layer
covering the substrate, wherein a plurality of extrusions are
formed on a portion of a surface of the N-type semiconductor layer,
and a channel is formed between every two adjacent extrusions of
the plurality of extrusions; forming an active layer covering the
plurality of the extrusions; forming a P-type semiconductor layer
covering the active layer; forming a transparent contact layer
covering the P-type semiconductor layer; forming an N-type
electrode layer which adheres to the N-type semiconductor layer and
is located in the channel; forming a plurality of P-type electrodes
adhering to a portion of a surface of the transparent contact
layer; forming an insulating layer covering the transparent contact
layer and the N-type electrode layer, wherein a portion of the
N-type electrode layer is exposed to be an N-type pad; and forming
a conductive layer which covers the insulating layer and is
connected to the P-type electrodes, wherein at least one P-type
electrode of the P-type electrodes is a P-type pad.
15. The method of making the light emitting diode according to
claim 14, wherein the material of the substrate is selected from a
group consisting of sapphire and glass.
16. The method of making the light emitting diode according to
claim 14, wherein the shape of the extrusions is rectangular
prism.
17. The method of making the light emitting diode according to
claim 14, wherein the material of the N-type semiconductor layer,
that of the P-type semiconductor layer, and that of the active
layer are selected from a group consisting of GaN, AlGaN, InGaN,
and AlInGaN.
18. The method of making the light emitting diode according to
claim 17, wherein the structure of the active layer is selected
from a group consisting of double hetero-junction structure and
quantum well structure.
Description
FIELD OF THE INVENTION
The present invention relates to a structure of a light emitting
diode (LED) and a method of making the same, and more particularly,
to a structure of a light emitting diode with the P electrode and
the N electrode mutually intercrossed, and a method of making the
same.
BACKGROUND OF THE INVENTION
In recent years, a great deal of attention has been directed to the
light-emitting device utilizing gallium nitride-based
semiconductors such as GaN, AlGaN, InGaN, and AlInGaN. Usually,
most of the light-emitting devices of the aforementioned type are
grown on an electrically insulating sapphire substrate, which is
different from other light-emitting devices utilizing a conductive
substrate. Since the sapphire substrate is an insulator, the
electrodes cannot be directly formed on the substrate directly, and
has to directly contact the P-type semiconductor layer and the
N-type semiconductor layer individually so as to complete the
manufacturing of the light-emitting device formed on the sapphire
substrate.
Please refer to FIG. 1 and FIG. 2, wherein FIG. 1 is a diagram
showing the top view of the conventional light emitting diode made
from the gallium nitride-based semiconductor, and FIG. 2 is a
diagram showing the cross-sectional view taken from the a-a' line
in FIG. 1. Such as shown in FIG. 1 and FIG. 2, an N-type GaN layer
20, an active layer 40, a P-type GaN layer 60, and a transparent
contact layer 80 are sequentially formed as a stacked structure on
a sapphire substrate 10. The aforementioned active layer 40 is made
of GaN, AlGaN, InGaN, or AlInGaN having a double hetero-junction
structure or a quantum well structure. Thereafter, an etching
process is performed to expose a portion of the N-type GaN layer
20. Then the N electrode 70 and the P electrode 90 are formed
respectively on the exposed surface of the N-type GaN layer 20 and
on the surface of the transparent contact layer 80.
The aforementioned FIG. 1 and FIG. 2 show the conventional light
emitting diode made from the gallium nitride-based semiconductor
with small chip size. Generally, the actual size of such light
emitting diode with small chip size is 10 mil.times.10 mil, or 8
mil.times.8 mil. When the size of the light emitting diode is
larger than 10 mil.times.10 mil, such as 20 mil.times.20 mil (i.e.
the area is 400 mil.sup.2), such light emitting diode belongs to
the category of big chip size.
The sizes of P electrode and N electrode of the conventional light
emitting diode with big chip size are not enlarged in accordance
with the chip size. The reason resides in that the P electrode and
the N electrode have the nature of blocking light. Hence, if the
size of P electrode and that of the N electrode are enlarged as the
size of the chip is enlarged, the light emitting efficiency of the
light emitting diode with big chip size will be reduced. Therefore
the conventional light emitting diode with big chip size utilizes
another method for designing the P electrode and the N electrode.
Please refer to FIG. 3, wherein FIG. 3 shows the top view of the
conventional light emitting diode with big chip size. Since FIG. 3
merely shows the top view, only part of the elements of the
conventional light emitting diode with big chip size can be
illustrated in FIG. 3. Those elements shown in FIG. 3 are an N-type
GaN layer 120, an N electrode 170, a transparent contact layer 180,
and P electrode 190 wherein the N electrode 170 is located on a
portion of the N-type GaN layer 120; the transparent contact layer
180 is located on another portion of the N-type GaN layer 120; and
the P electrode 190 is located on the transparent contact layer
180. Moreover, in FIG. 3, an N pad 175 and a P pad 195 are further
used as contacts for use in the connection of external wiring.
According FIG. 3, the conventional light emitting diode with big
chip size is featured in a plurality of striped N electrodes 170
and P electrodes 190, and any two stripes of N electrodes 170 and P
electrodes 190 are not mutually intercrossed. Besides this method
can prevent the serious light blocking caused by the too large
total electrode area, it can promote the evenness of current
distribution. However, although this design has its own merits, yet
its size is fixed, so that it lacks of the possibility for change
in accordance with the actual demands.
SUMMARY OF THE INVENTION
Just as described above, the design of the conventional light
emitting diode with big chip size still has room for improvement.
Hence, an objective of the present invention is to provide a
structure of a light emitting diode and a method of making the
same, wherein the structure design is based on a unit chip, whereby
the light emitted by each unit chip is more even and the operating
voltage of the device is reduced.
Another objective of the present invention is to provide a
structure of a light emitting diode and a method of making the same
wherein all the P electrodes and the N electrodes on the wafer are
respectively connected in series, whereby the cut size of the
device can be enlarged arbitrarily according to the size of the
unit chip.
Still another objective of the present invention is to provide a
structure of a light emitting diode and a method of making the
same, whereby the light emitting efficiency is increased.
According to the aforementioned objectives of the present
invention, the present invention provides a structure of a light
emitting diode comprising: a substrate; a semiconductor epitaxial
structure comprising an N-type semiconductor layer, an active
layer, and a P-type semiconductor layer, wherein the N-type
semiconductor layer covers the substrate, and a plurality of
extrusions are formed on a portion of a surface of the N-type
semiconductor layer, and a channel is formed between every two
adjacent extrusions, and the active layer and the P-type
semiconductor layer are stacked in sequence on the extrusions; an
N-type electrode layer which adheres to the N-type semiconductor
layer and is located in the channel; and a plurality of P-type
electrodes located above the P-type semiconductor layer. Moreover,
the structure of the light emitting diode according to the present
invention further comprises a transparent contact layer located
between the P-type semiconductor layer and the P-type electrodes.
Furthermore, the structure of the light emitting diode according to
the present invention further comprises an insulating layer
covering the transparent contact layer and the N-type electrodes,
wherein a portion of the N-type electrode layer is exposed to be an
N-type pad; and a conductive layer that covers the insulating layer
and is connected to the P-type electrodes, wherein at least one
P-type electrode of the P-type electrodes is a P-type pad.
Furthermore, according to the aforementioned objectives of the
present invention, the present invention provides a method of
making the above structure of a light emitting diode. The method
comprises the following steps: firstly, providing a substrate;
then, forming an N-type semiconductor layer covering the substrate,
wherein a plurality of extrusions are formed on a portion of a
surface of the N-type semiconductor layer and a channel is formed
between every two adjacent extrusions; then, forming an active
layer covering the extrusions; then, forming a P-type semiconductor
layer covering the active layer; then, forming a transparent
contact layer covering the P-type semiconductor layer; then,
forming an N-type electrode layer which adheres to the N-type
semiconductor layer and is located in the channel; then, forming a
plurality of P-type electrodes adhering to a portion of a surface
of the transparent contact layer; then, forming an insulating layer
covering the transparent contact layer and the N-type electrodes,
wherein a portion of the N-type electrode layer is exposed to be an
N-type pad; and then forming a conductive layer which covers the
insulating layer and is connected to the P-type electrodes, wherein
at least one P-type electrode of the P-type electrodes is a P-type
pad.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing aspects and many of the attendant advantages of this
invention will become more readily appreciated as the same becomes
better understood by reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein:
FIG. 1 is a diagram showing the top view of the conventional light
emitting diode made from the gallium nitride-based
semiconductor;
FIG. 2 is a diagram showing the cross section viewed along the a-a'
line in FIG. 1;
FIG. 3 is a diagram showing the top view of the conventional light
emitting diode with big chip size;
FIG. 4 is a diagram showing the top view of the light emitting
diode with big chip size according to an embodiment of this
invention; and
FIG. 5 is a diagram showing the cross section viewed along the b-b'
line in FIG.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The structure of light emitting diode and the method of making the
same of this invention are suitable for the light emitting diode
having the area that is larger than 100 mil.sup.2, the light
emitting diode also having the insulating substrate, and the
present invention is featured in that the P electrode and the N
electrode are mutually intercrossed. Please refer to FIG. 4 showing
the top view of the light emitting diode with big chip size
according to an embodiment of this invention. The single one light
emitting diode with big chip size according to this invention is
the unit chip 200 in FIG. 4. The size of the unit chip 200 is about
40 mil.times.40 mil. That is, the length of the unit chip 200 is 4
times as much as the length 10 mil of the conventional light
emitting diode, and the area of the unit chip 200 is 16 times as
much as the area 100 mil.sup.2 of the conventional light emitting
diode. However, this invention is not limited thereto. In fact,
this invention is suitable for the condition that the area of the
unit chip 200 is larger than 100 mil.sup.2, wherein formerly a
plurality of P electrodes and N electrodes had to be added if the
conventional method as shown in FIG. 3 were adopted. Hence, the
size of the unit chip 200 is not necessarily 40 mil.times.40 mil.
For example, the size of the unit chip 200 may be 10 mil.times.20
mil, 10 mil.times.40 mil, 20 mil.times.20 mil, and so on.
Since FIG. 4 is the top view, only part of the elements of the unit
chip 200 can be illustrated in FIG. 4. Those elements shown in FIG.
4 are an N-type semiconductor layer 220, an N-type electrode layer
270, a transparent contact layer 280, a plurality of P-type
electrodes 290, and a conductive layer 300. Moreover, an insulating
layer is omitted in FIG. 4 to clearly show the elements hidden
under the insulating layer, such as the N-type semiconductor layer
220, the N-type electrode layer 270, and the transparent contact
layer 280. Concerning the positional relationship between the
insulating layer and other elements, please refer to FIG. 5 that
will be described in details later.
Concerning FIG. 4, the N-type electrode layer 270 is located on a
portion of the N-type semiconductor layer 220, and the transparent
contact layer 280 is located on another portion of the N-type
semiconductor layer 220, and a plurality of P-type electrodes 290
are located on the transparent contact layer 280. Moreover, the
conductive layer 300 is used to connect the P-type electrodes 290
that are originally separated. Furthermore, in FIG. 4, an N-type
pad 275 and a P-type pad 295 are respectively connected to the
N-type electrodes 270 and the conductive layer 300, whereby the
N-type pad 275 and the P-type pad 295 can be used as contacts to
which the external wirings are connected.
Please refer to FIG. 5 showing the cross section viewed along the
b-b' line in FIG. 4 to understand more clearly the connection
relationship between the elements of the unit chip 200. The unit
chip 200 in FIG.5 comprises: a substrate 210, the N-type
semiconductor layer 220, an active layer 240, a P-type
semiconductor layer 260, the N-type electrode layer 270, the N-type
pad 275, the transparent contact layer 280, the P-type electrodes
290, the P-type pad 295, an insulating layer 330, and the
conductive layer 300. It can be seen in FIG. 5 that the N-type
semiconductor layer 220 covers the substrate 210, wherein a
plurality of extrusions 310 are formed on a portion of the surface
of the N-type semiconductor layer 220, and the shape of the
extrusions is such as a rectangular prism. Moreover, a channel 320
is formed between the extrusions 310. Furthermore, the
aforementioned substrate 210 is made of the insulating material,
such as sapphire or glass, and the material of the N-type
semiconductor layer 220 is: such as GaN, AlGaN, InGaN, or
AlInGaN.
In addition, the active layer 240, the P-type semiconductor layer
260, and the transparent contact layer 280 are stacked in sequence
from the bottom to the top on the aforementioned extrusions 310.
Besides, the active layer 240 is made of the material such as GaN,
AlGaN, InGaN, or AlInGaN with a double hetero-junction structure or
a quantum well structure. Moreover, the P semiconductor layer 260
is also made of the material such as GaN, AlGaN, InGaN, or AlInGaN,
and the transparent contact layer 280 is made of the transparent
and conductive material to satisfy the demands of being permissible
to light and being conductive electrically.
Furthermore, the N-type electrode layer 270 adheres on a portion of
the N-type semiconductor layer 220 in the channel 320, and the
P-type electrodes 290 adheres on a portion of the surface of the
transparent contact layer 280. Besides, the insulating layer 330
covers the exposed bottom of the channel 320, the exposed
transparent contact layer 280, and the exposed N-type electrode
layer 270, but a portion of the N-type electrode layer 270 is still
exposed to be an N-type pad 275 as a contact of the unit chip 200
for use in the connection of external wirings. In addition, the
conductive layer 300 covers the insulating layer 330 and is
connected to the P-type electrodes 290, wherein at least one P-type
electrode 290 is used to be a P-type pad 295 as another contact of
the unit chip 200 for use in the connection of external
wirings.
In addition to the aforementioned structure of the light emitting
diode, the present invention further provides a method of making
the light emitting diode, the method comprising the following
steps. Firstly, the substrate 210 is provided. Next, the N-type
semiconductor layer 220 is formed to cover the substrate 210,
wherein the extrusions 220 are formed on a portion of a surface of
the N-type semiconductor layer 220, and the channel 320 is formed
between the extrusions 310.
Then, the active layer 240, the P-type semiconductor layer 260, and
the transparent contact layer 280 are stacked sequentially form the
bottom to the top on the aforementioned extrusions 310. Next, the
N-type electrode layer 270 is formed to adhere to a portion of the
N-type semiconductor layer 220 in the channel 320. Then, the P-type
electrodes 290 are formed to adhere to a portion of the transparent
contact layer 280. Then, the insulating layer 330 are formed to
cover the exposed bottom of the channel 320, the transparent
contact layer 280, and the N-type electrode layer 270 portion of
which is still exposed. This exposed portion of the N-type
electrode layer 270 is the N-type pad 275 used as a contact of the
unit chip 200 for use in the connection of external wirings. Next,
the conductive layer 300 is formed to cover the insulating layer
330 and connected to the P-type electrodes 290, wherein at least
one of the P-type electrodes is used to be the P-type pad 295 as
another contact of the unit chip 200 for use in the connection of
external wirings.
To sum up, the structure of the light emitting diode is featured in
that the N-type electrode layer 270 and the conductive layer 300
connected to the P-type electrodes 290 are mutually intercrossed,
according to the top view of FIG. 4. However, as a matter of fact,
the N-type electrode layer 270 is located under the P-type
electrodes 290 and the conductive layer 300, wherein the insulating
layer 330 (FIG. 5) is used therebetween to separate the N-type
electrode layer 270 and the conductive layer 300 so as to avoid
mutual contacts causing short-circuiting. Moreover, one advantage
of the present invention is to provide a structure of a light
emitting diode and a method of making the same, wherein the
structure is designed for a unit chip, whereby the light emitted by
each unit chip is more even, and the operating voltage of the
device is reduced.
Another advantage of the present invention is to provide a
structure of a light emitting diode and a method of making the
same. With the use of the present invention, all the P electrodes
and the N electrodes on the wafer are connected in series
respectively, whereby the cut size of the device can be enlarged
arbitrarily according to the size of the unit chip.
Still another advantage of the present invention is to provide a
structure of a light emitting diode and a method of making the
same, whereby the light emitting efficiency is increased. Herein
the light emitting efficiency stands for the luminance of the light
emitting diode per unit of electrical power dissipated. Due to the
present invention having the channel 320 (FIG. 5) in the light
emitting diode with big chip size, the counts of the total
reflection of light are reduced, so that and the light can be
emitted from the channel 320 earlier, thereby increasing the light
emitting efficiency of the light emitting diode.
As is understood by a person skilled in the art, the foregoing
preferred embodiments of the present invention are illustrations of
the present invention rather than limitations of the present
invention. It is intended to cover various modifications and
similar arrangements comprised within the spirit and scope of the
appended claims, the scope of which should be accorded the broadest
interpretation so as to encompass all such modifications and
similar structure.
* * * * *